Papers by Scientific Journal of Aerospace Mechanics
Imam Hossein University, 2022
In the analysis of many offshore structures such as oil columns and structures, oil rig abutments... more In the analysis of many offshore structures such as oil columns and structures, oil rig abutments and towers surrounded by water, the cantilever beam model is usually used. These models usually bear the weight of a concentrated mass, and the response amplitude of these structures is of particular importance during design. In this paper, a nonlinear beam immersed in a fluid with a concentrated mass under the effects of the harmonic flow of water has been studied. Using the harmonic balancing method, the response of a nonlinear beam with three nonlinear terms is determined in the first four modes. Examination of the frequency response by analytical solution and numerical simulation shows that the jump phenomenon occurs in the triple response zone between the bifurcation points. The jump phenomenon is hardening in the first mode and softening in the second to fourth modes. Each of the nonlinear sentences has different effects on the vibrational behavior of the system and the jump phenomenon. The behavior of the beam in the state space along with the time response and Poincaré mapping shows that the path of the phase curve has different stability points. Finally, the phenomenon of chaos in the nonlinear beam was studied. At the bifurcation points, the behavior of the system is chaos, and the geometric nonlinear sentence has the most effective effect on the response disorder. Investigating the jump phenomenon using analytical and numerical methods and comparing the two methods with each other to validate the results, study the jump phenomenon in the fourth mode, comprehensive study of nonlinear phenomena such as bifurcation and chaos in phase curves, time response, poincaré, and mapping, are an innovation in the field of the immersed nonlinear beam.
Imam Hossein University, 2022
In this research, the free vibration of rotating tapered Timoshenko beam with piezoelectric layer... more In this research, the free vibration of rotating tapered Timoshenko beam with piezoelectric layer has been studied. It is assumed that the beam is made of Functionally Graded Materials (FGM) through the thickness direction and the boundary condition is a cantilever attached to the hub. The first-order shear deformation theory has been used to drive governing equations. At first, the total energy of the system such as potential and kinetic energies for the beam and piezoelectric layer has been derived, and then the natural frequencies of the beam have been determined by the Ritz approach based on minimizing the total system energy. After verifying the results by comparing them with other research, the effects of some parameters such as hub radius, rotational speed, taper ratios, rotary inertia, material gradient, piezoelectric voltage, and beam thickness on the natural frequencies of the tapered Timoshenko beam have been studied in detail. The results showed that with increasing the angular velocity of the beam, the natural frequency increases so that as the increasing velocity increases, the natural frequency increases with a steeper slope.
Imam Hossein University, 2022
In this study, the effect of the ratio of different nanoparticle compositions on the viscosity pe... more In this study, the effect of the ratio of different nanoparticle compositions on the viscosity performance of the base oil is investigated. The aim of this study is to achieve the characteristics of optimal nanolubricants. The experiments are performed at temperatures of 5-55°C, volume fractions of 0.05-1% and shear rates of 665.5-10664s-1. Experimental results showed that nanofluids have a non-Newtonian and quasi-plastic behavior. The maximum viscosity reductions are obtained for MWCNT / Al2O3 (10%: 90%) - 10W40 and MWCNT / Al2O3 (40%: 60%)-10W40 at -8.13% and -10.85%, respectively. The results show that MWCNT/Al2O3(10%:90%)/10W40 nanofluids have better lubrication performance at engine start (lower oil viscosity) and engine movement (more controlled behavior) than competing nanofliud. Using the response level method, to predict the target response data, a normalized three-variable-three-degree model with the characteristics of the power transfer function, λ = -0.15 and a constant value equal to zero is presented. Margin of deviation is in the range of -2.72 %<MOD<2/66 %. More viscosity sensitivity also occurred at higher volume fractions.
Imam Hossein University, 2022
In this paper, an adaptive fuzzy extended state observer is proposed to estimate the states and e... more In this paper, an adaptive fuzzy extended state observer is proposed to estimate the states and external disturbances simultaneously for Single-Input-Single-Output nonlinear affine systems. The observer gains are time-varying and adjusted using an adaptive law. The Takagi-Sugeno fuzzy system is used for modeling that, unlike Mamdani methods, provides a more precise and comprehensive analysis. The proposed adaptive fuzzy observer is designed to relax the limitations of the extended state observers and improve system performance as compared to the classical methods in presence of time-varying disturbances. Moreover, the stability of the proposed method and the convergence of the estimation error are analyzed using the Lyapunov stability Theory. The performance of the proposed method is shown in simulations of control of the inverted pendulum. The simulation results, as compared to the non-adaptive fuzzy observer, show better performance in terms of transient and steady-state responses, control input amplitude, and robustness in presence of measurement noise and external disturbances.
Imam Hossein University, 2022
Shape memory alloys (SMAs) are a special kind of smart materials with an intrinsic shape memory e... more Shape memory alloys (SMAs) are a special kind of smart materials with an intrinsic shape memory effect. This characteristic brings up SMAs as an actuator in dynamic mechanisms. These materials can recover their initial length under special thermal operations. This paper deals with fuzzy-PID control of contrary mechanisms actuating with a pair of SMA wires. The Brinson model combined with Elahinia’s conditions is employed to describe the phase transformation models. By combining Newton's second law, transformation models, heat transfer, and strain relations, the governing equations of the contrary mechanism are derived. Due to the nonlinear behavior of SMA actuators, the non-model-based controllers are preferred compared to the model-based ones. Therefore, the fuzzy-PID control method is employed to control the position of the closed-loop system. The fuzzy rules are defined such that the coefficients of the PID controller are tuned according to the system response. Both numerical and experimental results are provided to illustrate the effectiveness of the proposed approach. It will be shown that under the proposed method, the tracking error will converge to zero asymptotically.
The Brinson model combined with Elahinia's conditions is employed to describe the phase transfo... more The Brinson model combined with Elahinia's conditions is employed to describe the phase transformation models. Both numerical and experimental results are provided to illustrate the effectiveness of the proposed approach. It is shown that under the proposed method, the tracking error converges to zero asymptotically.
Imam Hossein University, 2022
Physical systems often contain constraints and limitations. Actuator rate saturation is one of th... more Physical systems often contain constraints and limitations. Actuator rate saturation is one of these limitations that has adverse effects on the flight control system which increases the oscillating response and thus the instability of the system. Actuator rate saturation is one of the main reasons for pilot-induced oscillations (PIOs). This paper proposes a model predictive control algorithm with two degrees of freedom structure to prevent the destructive effects of actuator rate saturation on the flight control system. Also, by obtaining starting point of the opening loop position in the flight system and the frequency at which the actuator rate saturation is activated for the first time, the saturation effects are well predicted. Then, by introducing an analytical method similar to one of the conventional methods of robust control known as the loop shaping method, the proposed model predictive controller parameters are adjusted and the stability and robustness of the closed loop system against the uncertainty of the controller parameters are investigated. In this method, by obtaining robust patterns, an attempt has been made to shape it in such a way that disturbances and noise are suppressed in a frequency range. It is also shown how the controller and pilot work by using a switch. Finally, the designed controller is compared with the proportional-integral-derivative controller (PID) that is common in the industry, and its advantages are shown.
Imam Hossein University, 2022
Constant loading causes creep deformation in polymer-based adhesives due to their visco-elastic n... more Constant loading causes creep deformation in polymer-based adhesives due to their visco-elastic nature. The aim of this study was Investigating the effect of 2-D defects on tensile and creep behavior of single-lap ceramic-metal joints (SLJs) manufactured with adhesive Aqua-Flex. Static tensile test was performed at three ambient temperatures, 40°C and 60°C for flawless and defected adhesive joints in ceramics as well as defects in ceramics and aluminum, and then by applying final stress-to-strength ratios equal to 0.40 and 0.60, tensile creep test has been also performed. By increasing the final stress-to-strength ratio from 0.40 to 0.60 at ambient temperature, the creep displacement for flawless connection is 36%, this amount increases to 33% for defected ceramics and to 40% for ceramics with more defections. At 40°C and 60°C, respectively, this increase is 35% and 18% for defected connection, 54% and 5% for defected connection in ceramic and 39% and 42% for connection with defected connection in ceramic and aluminum. Also, as the temperature increases from ambient temperature to 60°C, the breaking force for the three types of connections is reduced by 46%, 25% and 80%.
Imam Hossein University, 2022
Proportional Navigation is commonly used in the terminal phase of homing missiles. To implement t... more Proportional Navigation is commonly used in the terminal phase of homing missiles. To implement this guidance law, it is necessary to measure or calculate Line of Sight (LOS) rate. It is usually necessary to use gimballed seekers to measure the LOS rate. However, if the system is equipped with a strapdown seeker, the LOS rate must be calculated from derivation or estimation methods. Because the signal measured by seekers usually contains noise, so deriving this signal requires a low pass filter that will cause the behavior changes in the measured variable. The issue in this paper is the design of a discrete time sliding mode extended state observer to estimate the LOS rate and evaluate it in the guidance loop. This is done by performing computer simulations. Implementing continuous time observers in processors has challenges such as sampling time selection and it is better to design the observer in discrete time form from the beginning so that its implementation issues can be considered from the design level and in computer simulations.
Imam Hossein University, 2022
Rollover which causes a large number of deaths and pecuniary damages is one of the basic challeng... more Rollover which causes a large number of deaths and pecuniary damages is one of the basic challenges in vehicle safety. If we can decrease the possibility of rollover in some conditions, probably other important indices are decreased like vehicle stability. It means that some indices are improved through the change of parameters but some of them are not. For this reason, to improve rollover and stability indices simultaneously, combined Topsis-Taguchi and Shannon Entropy methods were used in this paper. First, a whole vehicle as a dynamic model was chosen and to verify the most important parameters, 13 parameters in 3 levels including geometric and volumetric parameters were verified. 27 series of tests through the Taguchi method in Minitab software were prepared and evaluated in Carsim software for obtaining rolling angles and yaw rate around the Z axle. The six most important parameters in the previous level were distinguished and again 25 tests were conducted through the Taguchi method in 5 stages in Carsim Software and multi-objective optimization was conducted. Results showed the suggested method in 80km/h made rollover index, rolling angle, lateral acceleration, and yaw rate around Z axle be decreased as %28.9, %26.2, %0.3, %0.2, respectively. Again, the tests were conducted at different speeds and it was found that with increasing speed, the improvement percentage of all indicators decreases.
Imam Hossein University, 2022
In the present study, the dynamic response of rectangular steel plates under repeated impulsive l... more In the present study, the dynamic response of rectangular steel plates under repeated impulsive loading was investigated. In this regard, experiments were performed on three different structures: unstiffened, stiffened with one and two welding lines. To investigate the deformation modes and the failure mechanism of the experimental specimens, dynamic loads in a wide range were applied up to 3 loads by 25, 35, 45, and 50 g charge masses. Experimental observations demonstrate that with increasing charge mass, the Mode Ia and Mode Ib are observed in a higher charge mass and loading repetitions in a higher number. For the unstiffened plate, at the 3rd load with a mass of 25g, a change Mode Ia is observed, however, the same deformation mode occurs for the stiffened plate with a single and two weld lines at the 3rd blast load by 35g and 45 g charge mass, respectively. These observations indicate the effect of the weld line and its numbers on the variation of failure modes. Furthermore, in the numerical modeling section, the Group Method of Data Handling (GMDH) neural network was used to present a mathematical model based on dimensionless numbers to predict the maximum permanent deflection of tested specimens. Good agreement between the proposed model and the corresponding experimental results is obtained and all data points are within the ±10% error range for every two pattern.
Imam Hossein University, 2022
In this paper, governing equilibrium equations for thin and thick-walled cylindrical shells based... more In this paper, governing equilibrium equations for thin and thick-walled cylindrical shells based on the classic membrane and bending theories of shells using the first order shear deformation theory (FSDT) and the third order shear deformation theory (TSDT) in the three dimensional theory of elasticity for simply supported boundary conditions according to the buckling mode shapes for axial, circumferential and radial displacement field and subjected to axial and uniform external pressure buckling load have been derived. Then, the set of governing buckling equations of the shell for the axial, circumferential and radial displacements are numerically solved to obtain axial and circumferential critical buckling load. Moreover, to verify obtained results the shell subjected to axial buckling load has been modeled in ANSYS finite element software. The accuracy of obtained result to predict the critical axial load and external pressure buckling loads of the thin and thick shells have been compared with each other and the ones reported in the literature.
Imam Hossein University, 2022
In this paper, a robust hybrid control approach for vibration and attitude
control of a flexible ... more In this paper, a robust hybrid control approach for vibration and attitude
control of a flexible rotating structure as a fully coupled rigid-flexible
system is investigated. Two control algorithms as a combination of secondorder
super twisting-nonsingular terminal sliding mode control (SMC)
considering external disturbances and system uncertainties are developed.
The nonlinear dynamic equation of the motion is derived via the
Lagrangian approach and the finite element method. The non-singular
terminal SMC leads to high accuracy in target tracking, and convergence
and the super twisting part significantly reduce the chattering
phenomenon. The overall stability of the system has been guaranteed using
the Lyapunov theory. The simulations in the form of a comparative study
(with agility, accuracy, and high convergence criteria) show the feasibility
of performing large-angle maneuvers and significantly reducing the
vibrations caused by the flexible parts. Moreover, by controlling the
chattering phenomenon, the system performance regarding highfrequency
modes excitation is increased.
Imam Hossein University, 2022
In this study, by using Molecular Dynamics (MD) simulations, the effect of adhesion on the remova... more In this study, by using Molecular Dynamics (MD) simulations, the effect of adhesion on the removal and separation of materials in the nano-scale has been studied numerically during the nano-scratching test. The virtual setup simulates the scratching of a flat substrate made of a single crystalline aluminum using a rigid conical indenter with a blunted spherical tip (radius of 20 nm) at four different scratching depths (i.e., 0, 3, 7, and 10 A) was studied. The classical Lenard-Jones interatomic potential is used to model and regulate the adhesion between the atoms of the indenter and the substrate, which change from 5% to 70% of the interatomic adhesion strength of aluminum atoms. This mimics the effect of the lubricant without modeling. Although the effect of adhesion has been consistently neglected in previous studies, it has been observed that in scratches with shallower depths, the adhesive will have a significant effect on friction and wear. It is worth noting that in this study, due to the effect of plasticity being the main mechanism of the wear, according to experimental observations, friction and wear have a linear relationship with each other.
Imam Hossein University, 2022
In the current research study, the large plastic deformations of similar and dissimilar single- a... more In the current research study, the large plastic deformations of similar and dissimilar single- and multi-layered metallic plates with the same areal density under repeated uniform impulsive loading have been investigated. The ballistic pendulum along a 200 mm length standoff blast tube was used to apply the blast load on the specimen. Forty testing specimens in three different layering configurations including single-, double, and triple-layered, and eight different arrangements were considered. For the same loading and experimental condition, 10 g plastic explosive was utilized and the dynamic response of structures was studied for up to five consecutive loads. The experimental results indicated large plastic global deformation with thinning happening at the clamped boundary and also tearing for some experiments. The results also represented that the maximum permanent deflections of plates were increased by the number of blast loads and the progressive deflection of the plates at the center decreased exponentially with increasing the number of blasts. Placing a thick front layer and a thin back layer gives better blast performance to the tested specimen against repeated impulsive loading. The obtained result for multi-layered configurations with the same material is completely consistent with those structures made of dissimilar layers.
Imam Hossein University, 2022
The sled system is used to test anti-penetration structures, ejection seat, and spacecraft equipm... more The sled system is used to test anti-penetration structures, ejection seat, and spacecraft equipment that its technology is owned by a few developed countries. In this research, the dynamic analysis of applied forces on the system has been investigated. The effective forces on the sled include propulsive force, drag force, lift force, and friction force, which are all variable. To obtain the propulsive force according to the functional and geometric specifications of the designed sled, the grain engine design has been carried out to reach 0.85 Mach in a second. After extracting the governing equations for extracting the propulsive force, the changes of the propulsive force during the combustion time were obtained and formulated. At the next step, numerical simulation is used to obtain the lift and drag forces and after validating the numerical solution with experimental research, the values of drag and lift forces at different speeds are extracted and formulated. Next, due to sled mass variations during the combustion step, the friction force between the rail and the slipper is obtained. Finally, the differential equation and dynamic behavior of the system are analyzed. The results show the highest pressure is applied to the inner part of the slipper, which can lead to wear and damage of the rail surface at high speeds and lead to the sled deviating from the rail track. Also, the amount of friction force is negligible in comparison with other forces.
Imam Hossein University, 2022
In this study, the vibrational behavior of V shaped AFM beam by supposing poly vinyl alcohol (PVA... more In this study, the vibrational behavior of V shaped AFM beam by supposing poly vinyl alcohol (PVA) nanofibers scaffolds with different formats and PVA concentrations as the soft samples has been investigated. Based on the importance of polyvinyl alcohol nanofibers and their application in medical sciences and industry, it seems necessary to consider an independent study on the vibrational behavior of atomic force microscope cantilevers considering polyvinyl alcohol nanofibers. After making of PVA nanofibers scaffolds with different formats and PVA concentrations by electrospinning system, the elasticity modules and adhesions of the samples have been earned in extend and retraction strokes as the most important step to study the vibrational behavior of the AFM beam. To investigation for the mechanical behavior of PVA nanofibers scaffolds with different formats JPK SPM (version spm-5.0.96) software has been used. By increasing the PVA concentration, the elasticity modules increase, but adhesion decreases. Appling the extend strokes increases the elasticity modules, but decrease the adhesion. For theoretical dynamic behavior of V shaped AFM beam, Timoshenko bema theory has been applied. In the present study, the elastic modulus of poly vinyl alcohol (PVA) nanofibers scaffolds with different formats and PVA concentrations has been defined using AFM, then the vibrational behavior of V shaped AFM cantilever by supposing PVA nanofibers as the soft sample has been studied using finite element modeling (FEM) and experimental method. The obtained results by FEM modeling show that increasing the elasticity modules of the samples increases the resonant frequency and amplitude of FRF of vertical movement of the beam. The results by theoretical modeling have been compared with experimental method. The results show excellent agreement.
Imam Hossein University, 2022
Imam Hossein University, 2022
Tracking aerial objects using conventional 2-DOF pedestals requires excessive angular acceleratio... more Tracking aerial objects using conventional 2-DOF pedestals requires excessive angular acceleration and velocity in the joints for some trajectories that pass through singular points. In this research, a 3-DOF redundant pedestal is proposed to solve such a problem. The redundant DOF increases the maneuverability and overall performance of the pedestal. Moreover, all of the possible trajectories can be tracked without facing any singularities. One of the main challenges in working with this redundant pedestal is that the inverse kinematic problem does not have a unique set of answers. In this paper, two optimization-based algorithms regarding limited joint velocities and limited joint accelerations are proposed to solve the inverse kinematic problem. In the limited joint velocities approach, a cost function of tracking error and joint velocities is formed and minimized. In the limited joint acceleration, on the other hand, joint velocities and accelerations are the elements that form the cost function. The simulation results for these algorithms are then compared with a conventional pseudo-inverse of the Jacobean approach. The criteria used to compare these methods are Integral of Squared Amplitude (ISA), Integral of Absolute Amplitude (IAA), Integral of Time-weighted Absolute Amplitude (ITAA), and Integral of Time-weighted Squared Amplitude (ITSA). The simulation results show the superiority of the limited joint acceleration method compared to the other two approaches.
Imam Hossein University, 2022
In this paper, a shell and tube heat exchanger used to transfer heat between two different fluids... more In this paper, a shell and tube heat exchanger used to transfer heat between two different fluids is simulated in three dimensions. This converter consists of a shell with 90 U-shaped tubes inside. For further heat transfer, the tubes were simulated and compared once without fins and again with fins, which are produced longitudinally and integrally with the tube body. The current flowing in the shell is MIL-PRF 23699 oil and the flowing fluid in the tubes is JP-4 fuel. These two fluids flow in separate and opposite directions and exchange heat with each other through contact with the surface of the tubes. Using Aspen software, the design is done in such a way that the heat exchanger has a shorter length and weight to have a better and higher effect on the efficiency of the helicopter. To investigate the effect of tube geometry and oil mass flow on the rate of heat transfer between fuel and oil, simulation has been performed in ANSYS Fluent program. In this simulation, a part of the whole heat exchanger is selected as the geometry and the effect of changing the geometry of the tubes, mass flow of fuel and oil on the heat transfer coefficient, Colburn coefficient, coefficient of friction and their ratio, and outlet temperature changes are investigated. The results of this simulation show that the heat transfer rate between fuel and oil for a heat exchanger with finned tubes is about 11% higher than without a fin. Also, reducing the mass flow of oil entering the shell increases the efficiency of the heat exchanger.
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Papers by Scientific Journal of Aerospace Mechanics
control of a flexible rotating structure as a fully coupled rigid-flexible
system is investigated. Two control algorithms as a combination of secondorder
super twisting-nonsingular terminal sliding mode control (SMC)
considering external disturbances and system uncertainties are developed.
The nonlinear dynamic equation of the motion is derived via the
Lagrangian approach and the finite element method. The non-singular
terminal SMC leads to high accuracy in target tracking, and convergence
and the super twisting part significantly reduce the chattering
phenomenon. The overall stability of the system has been guaranteed using
the Lyapunov theory. The simulations in the form of a comparative study
(with agility, accuracy, and high convergence criteria) show the feasibility
of performing large-angle maneuvers and significantly reducing the
vibrations caused by the flexible parts. Moreover, by controlling the
chattering phenomenon, the system performance regarding highfrequency
modes excitation is increased.
control of a flexible rotating structure as a fully coupled rigid-flexible
system is investigated. Two control algorithms as a combination of secondorder
super twisting-nonsingular terminal sliding mode control (SMC)
considering external disturbances and system uncertainties are developed.
The nonlinear dynamic equation of the motion is derived via the
Lagrangian approach and the finite element method. The non-singular
terminal SMC leads to high accuracy in target tracking, and convergence
and the super twisting part significantly reduce the chattering
phenomenon. The overall stability of the system has been guaranteed using
the Lyapunov theory. The simulations in the form of a comparative study
(with agility, accuracy, and high convergence criteria) show the feasibility
of performing large-angle maneuvers and significantly reducing the
vibrations caused by the flexible parts. Moreover, by controlling the
chattering phenomenon, the system performance regarding highfrequency
modes excitation is increased.